The present invention relates to the construction of reinforced concrete works, such as underground galleries, road tunnels, tunnels for underground railways, et cetera, employing prefabricated elements.
The construction of these works using prefabricated elements gives rise to a difficulty, because, in general, on the one hand, the weight of the elements is considerable, and on the other hand, the bulk of these elements renders their transport by road convoy difficult if not impossible.
It is a first aim of the present invention to overcome this difficulty, to lighten these prefabricated elements as much as possible and to reduce their external dimensions while retaining an internal finish as close as possible to the final finish, and thus to permit the performance of the method under particularly economical conditions.
A second aim of the invention is to achieve a continuity of the work by a second stage concreting executed on site astride the joints between the prefabricated elements. This continuity is fundamental, both from the standpoint of the mechanical strength and of the differential subsidences caused by traffic and from the standpoint of fluid-tightness. In order to achieve these aims, the method which is the subject of the invention is substantially characterized in that an open trench is first excavated, that hollow prefabricated concrete elements are then placed therein, consecutively and contiguously, each consisting of a frame, the external faces of which comprise reinforcements, that a filler concrete is poured covering the joints between elements and cooperating with the reinforced concrete of the elements and with the reinforcements so as to construct, in consecutive stages and rapidly, a monolithic work, the strength of which is appreciably greater than the respective strength of the prefabricated elements intially placed and of the filler concrete; and that a filling is finally executed.
In the performance of the method, the external reinforcements are fixed to the prefabricated element ("preframe") before the prefabricated element is placed.
An essential feature of the invention is the prefabricated reinforced concrete element itself, called "preframe", comprising the above-described characteristics.
In the case of a tunnel of prefabricated elements of very large dimensions, the preframes exhibit sizes which exceed the official road transport height limits.
In this case, the preframes are constructed in two or more complementary elements, which will be assembled on site afterwards.
The installation of the elements is effected either in an open trench excavated dry, or in consecutive transverse trenches excavated in thixotropic mud, particularly when the work has to be constructed on a dense urban site in streets or main roads near existing buildings.